The present invention relates to mechanisms for releasably clamping a tool holder to a support member. It is especially concerned with clamping mechanisms for clamping tool holders having hollow, tubular shanks. In this type of clamping mechanism, ball-like locking elements are commonly used to engage and hold the shank of the tool holder. One variation of this type of clamping mechanism employs an elongated lock rod which is reciprocally mounted in the support member. The lock rod generally includes two ramps so that when it is moved in a first direction, the ramps urge the locking elements radially outwardly to engage and hold the shank. Concave depressions adjacent the ramps permit the locking elements to move radially inward when the lock rod is moved in a second direction thus releasing the shank and permitting removal of the tool holder. Typically, the input force is applied along the axis of the lock rod. In some circumstances, on the other hand, the input force must be applied at an angle (usually 90.degree.) with respect to the axis of the lock rod. One such clamping mechanism is shown in U.S. Pat. No. 4,615,244 to Reiter, et al. The Reiter device includes a lock rod having a central passage extending therethrough. The inner walls of the central passage are formed with two opposing wedge faces. First and second cams, having cam faces adapted to engage the wedge faces on the lock rod, are moveable in a direction perpendicular to the axis of the lock rod. A screw type mechanism is provided for moving the cams towards or away from each other to effect longitudinal displacement of the lock rod.
A disadvantage associated with previous 90.degree. mechanisms employing a conventional wedge is that the sliding contact between wedge surfaces results in large frictional losses. Due to the frictional losses, the ratio of output force to input force is lowered thereby raising the torque or spring force needed to clamp the tool holder.
Another disadvantage with prior art devices is that the wedge angles are fixed. Sometimes it is necessary to change the wedge angle. For instance, if one wanted to reduce stroke, a steeper angle would be required. If one wanted to increase mechanical advantage, a shallower angle would be needed. In prior art devices, if the wedge angle on one component is changed, a corresponding change must be made in each of its mating components. Since a single component can not be changed without changing mating components, a greater number of parts must be maintained in inventory.
A further disadvantage of prior art designs relates to ease of manufacture. Prior art mechanisms which employ a conventional wedge present numerous manufacturing problems such as multiple setups and surface finishing. These manufacturing problems ultimately result in numerous inefficiencies and higher costs.